Synthesis method of lactide by confinement effect catalysis of crystalline porous polymer material

Abstract

The present invention discloses a synthesis method of lactide by confinement effect catalysis of crystalline porous polymer material, wherein the method comprising: (I) synthesis of catalyst; (II) synthesis of lactide by confinement effect catalysis; and (III) purification of lactide. In the present invention, a yield of L-lactide by catalysis of L-lactic acid by crystalline polymers is as high as 85.6%, which is 10% higher than the yield of lactide by H-β molecular sieve reported in documents currently available; it is easy to prepare the crystalline porous polymer material catalyst, which is environmental friendly, has a high yield and is recyclable, for consecutive 7 times the catalysis yield is maintained to be higher than 70%, and catalysis yield conservation rate is far higher than catalysis effects of catalysts reported in documents currently available.

The invention claimed is: 
     
       1. A synthesis method of lactide by confinement effect catalysis of crystalline porous polymer material, comprising following steps:
 step (I) synthesis of catalysts comprising: 
 a) placing a compound A, a compound B, mesitylene and 1,4-dioxane into a reaction vessel; 
 b) mixing the contents of the reaction vessel evenly; 
 c) adding acetic acid to the reaction vessel; 
 d) de-aerating the contents of the reaction vessel; 
 e) vacuum sealing the reaction vessel; 
 f) placing the reaction vessel in an oven for heating; 
 g) filtering precipitates from the reaction vessel; 
 h) washing the precipitates with a Soxhlet extractor; 
 i) vacuum drying the precipitates; and 
 j) obtaining solid catalysts; 
 wherein a structural formula of the compound A is: 
 
       
         
           
           
               
               
           
         
       
       wherein R 1  ═OH, CH 3 , OCH 3 , C 2 H 5 , F, Cl, Br or I; 
       wherein compound B is: 
       
         
           
           
               
               
           
         
         step (II) synthesis of lactide by confinement effect catalysis comprising: 
         a) adding the catalysts obtained in step (I), solvents, and lactic acid to a reaction vessel for reaction; 
         b) cooling down the reaction vessel slowly after the reaction; 
         c) filtering the contents of the reaction vessel after the reaction; 
         d) washing the contents of the reaction vessel after the reaction; 
         e) removing the solvents from the contents of the reaction vessel after the reaction at low pressure; and 
         f) obtaining crude lactide; 
         step (III) lactide purification comprising: 
         a) conducting liquid-liquid extraction on the crude lactide obtained in step (II) with methylbenzene and water, 
         b) combining organic phases of the liquid-liquid extraction, 
         c) removing the solvents of the combined organic phases at low pressure, and 
         d) obtaining lactide, 
         wherein in step (I) a mole ratio between the compound A and the compound B is 4:7; a volume ratio among the mesitylene, the 1,4-dioxane, and the acetic acid is 15:5:1; and a mole ratio between the compound A and the mesitylene is 1:25; 
         wherein in step (I) the method for de-aerating comprises freeze-pump-thaw cycling; 
         wherein in step (I) the conditions for heating in the oven comprise 80° C. for 3 days; 
         wherein in step (I) the conditions for washing with the Soxhlet extractor comprise specifically: washing four hours with THF and acetone; and conditions for vacuum drying comprise: 80° C. for 12 hours; 
         wherein lactic acid in step (II) comprises L-lactic acid of 90 percent purity; 
         wherein the solvents in step (II) comprise methylbenzene or ortho-xylene; wherein a mass ratio between the catalysts and the lactic acid is 1:10, and a weight/volume ratio of the catalysts and the solvents is 1:1 g/cm 3 ; 
         wherein reaction conditions in step (II) comprise: reaction time of 5 hr and reaction temperature 120° C.; 
         wherein in step (II) washing is done by washing with acetonitrile. 
       
     
     
       2. The synthesis method of lactide by confinement effect catalysis of crystalline porous polymer material according to  claim 1 , wherein the structural formula of the compound A is